CA2180605A1 - Acid-cleavable surfactants on the basis of alkylglycosides - Google Patents

Abstract

Disclosed is a novel acid-cleavable alkylglycoside-based surfactant of the formula:

(I) Also disclosed is a process for producing the surfactant by reacting an alkylglycoside of the formula:

(III) with an aldehyde or diacetal of the formula:

R2?CHO or (wherein R3 is a lower alkyl group) to form a cyclic acetal of the formula:

Description

- 1 - O.Z. 4956 Acid-cleavable surfactants on the basis of alkyl-qlycosides The invention relates to reaction products of alkyl-glycosides with aldehydes and/or diacetals of short-chain alcohols and aldehydes, the acetals obtained being alkoxylated. The invention further relates to a process for producing the abovementioned compounds and to the use of these compounds for preparing surfactants, especially for industrial detergents and cleaners.

The alkylglycoside surfactants according to the formula I of this invention are alkali-stable, low-foaming, cleavable into biodegradable fragments and exhibit altogether good wetting of hard surfaces.

With the relinquishment of solvents, especially chlorin-ated hydrocarbons, the use of which in dip-cleaning for degreasing was drastically curtailed in Germany by the Second Federal Pollution Control Act Regulations, there is now an increasing trend in many fields towards the use of aqueous, surfactant-containing systems. However, their lack of resistance to microbial attack is an urgent problem. At present, this problem is solved either by the addition/replenishment of appreciable amounts of bactericides or by using refractory or undegradable ingredients - primarily surfactants.

One approach to solving this problem is the use of cleavable surfactants which are initially biologically hard, i.e. non-biodegradable, in their use form and, after use, for example in metal baths or generally in the cleaning of hard surfaces, are converted into biodegrad-able fragments by simple operations. It is a further aimto cleave the surfactants to obtain an aqueous and an organic phase in such a way that the organic phase can be separated off together with the greasy dirt, thereby reducing the level of organic waste in the wastewater. In - 2 - O.Z. 4956 certain circumstances, it can even be of economic interest to work up the removed organic load and thereby recover substances of value ("rent a chemical").

The chemical concept for this envisages primarily branched surfactants having a pH-sensitive function as a predetermined breaking point. By changing the pH it is possible to cleave the surfactant into biodegradable fragments and at the same time achieve a phase separation into an organic phase with hydrophobic soil particles and lipophilic surfactant constituents and an aqueous phase.

The principle of pH-sensitive surfactants has for years been the subject of various papers and patents.

Industrial Launderer (July 1990, pp. 41 f) and also the technical information leaflet relating to Triton RW-Surfactant (July 1982) describe breaking stable emulsionsof oils and wastewater, which contain pH-sensitive surfactants, by addition of acids and separating off the oil phase. This process gives substantially oil-free wastewaters. The surfactants used are ethoxylation products of primary amines. It is true that products of this kind are known for,their good cleaning performance, but they are not biodegradable.

DE 42 27 894 describes a process for reducing organic constituents in wastewaters from industrial laundries by using various branched alkanolamine/amide ethoxylates.
The pH-sensitive surfactants described therein are said to be notable for a high cleaning performance, good separation from the emulsions in the event of a pH
change, and also good biodegradability. A disadvantage is the use of amine intermediates for synthesizing these compounds and the associated nitrosamine problem.

Jaeger et al., in JACS lll, 3001 - 3006, describe branched acetal surfactants prepared by reaction of long-chain fatty ketones with glycerol.
Trade-mark ~18060~
_ 3 _ O.z. 4956 Sokolowski, Piasecki et al., Tenside, Surf., Det. 30 (1993), 417, describe cleavable surfactants having an acetal group as pH-sensitive function. The acetal group is notable for high stability in a basic medium, while a cleavage occurs in the acid pH range. The disadvantage of the compounds described there are the costly starting materials.

It is an object of the present invention to provide cleavable surfactants which are free of the disadvantages described.
.

The starting materials should ideally comprise readily available, inexpensive materials based ideally on renew-able raw materials.

The cleavable surfactants should further have the follow-ing industrial cleaning properties profile:

1. low foam,2. alkali stability, 3. ~biological hardness' in their use form, 4. acid-cleavability into biodegradable substructures, and 0 5. high cleaning performance on hard surfaces in par-ticular.

The invention accordingly provides acid-cleavable alkyl-glycoside-based surfactants according to the general formula I

~060~

R ~ _ O

\O ~ ~ O -R
~ 1 O G
\G2 where R represents unbranched or branched alkyl and/or alkenyl groups having 1 to 20 carbon atoms, R represents alkyl groups having 6 to 20 carbon atoms, Gl represents (EO)V(PO)wH, G represents (EO) (PO)yH where EO = ethyleneoxy and PO = propyleneoxy, and v + w = 0-30, x + y = 0-30;

v + w + x + y >= 1.
The invention further provides a process for producing the acid-cleavable surfactants, a method of cleaning in technical processes using these acid-cleavable surfactants and their use.
Unbranched or branched alkyl and alkenyl groups R
include for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, n-dodecyl, n-tridecyl, isotridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-eiccsyl, oleyl, linolyl and linGlenyl. The alkyl and alkenyl groups described herein can of course be ~18060~

the corresponding mixtures. Preferably, Rl comprises saturated and little-branched alkyl groups having 1-14 carbon atoms.
Particular preference is given to Cl-C4-alkyl groups such as methyl and butyl and also unbranched C8-C14-alkyl groups which are commercially available in the form of their glycosides.
Advantageously, the compounds of the formula (I) are prepared by reacting alkylglycosides with aldehydes or - 4a -~180605 - 5 - O.Z. 4956 diacetals at temperatures of 50 - 200C in a vacuum in the presence of catalytic amounts of acid. The products are cyclic acetals between the aldehyde carbon atom and the glycoside OH groups in positions 4 and 6 of the glycoside (see the formula II). Another way of synthesiz-inq the surfactant compounds of the formula I according to this invention consists in the transacetalization of fatty aldehyde diacetals of fatty aldehydes and short-chain alcohols with the corresponding alkylglycosides.
This form of the reaction can be carried out under milder conditions than the direct acetalization.

~cto ~

~2_~o~ ~ ~ O, a~ - 2 (III) ~c2 a~"
. (II) The aldehydes used are representatives having a saturated C6-C20-alkyl chain; Examples are n-hexanal, n-heptanal, n-octanal, 2-ethylhexanal, n-nonanal, n-decanal, n-undecanal, n-dodecanal. Further representatives include all homologues having a branched C6-C20-carbon chain.
These are obtainable for example by hydroformylation of olefins having an internal double bond. Since the olefins used here generally have a random homologue and isomer distribution, it is convenient to refer to an average number of carbon atoms in relation to the radicals R2.

7~18060~

- 6 - O.Z. 4956 ~3 comprises short, unbranched or branched alkyl groups, for example methyl, ethyl, propyl, butyl.

As well as a direct acetalization, it is also possible, as described above, to carry out a transacetalization.
For this purpose, the aldehydes are first converted with alcohols into the corresponding diacetals. Here it is customary to use shorter alcohols, since the reaction is usually carried out in an excess of alcohol which has to be removed at the end by distillation. A further way of preparing dimethyl or diethyl acetals is the reaction of the aldehydes described with orthoesters (Houben-Weyl, Vol. 7, 4th Edition, pp. 417 ff.). Since these acetaliz-ation techniques are well known, they will not be more particularly described here.

The acetalization of the aldehydes, or the transacetaliz-ation of the aldehyde diacetals, with the alkylglycosides described can be carried out in the absence of a solvent.
An additional inert solvent or diluent is normally not necessary, but can be added if needed, for example in the event of viscosity problems.

Suitable catalysts include mineral acids such as, for example, HCl, H2SO4, H3PO4 or HCl04; organic carboxylic and sulphonic acids, for example methanesulphonic acid, p-toluenesulphonic acid, oxalic acid, formic acid, acetic acid, propionic acid, or Lewis acids such as, for example, BF3, AlCl3, ZnCl2 or TiCl4. The milder trans-acetalization may also be carried out using acidic clay minerals, for example R10. It is particularly advanta-geous to use p-toluenesulphonic acid as catalyst. The acidic catalyst is added in the amounts customary here, i.e. normally in an amount of about 0.1 - 5 mol%, based on the aldehyde component. A neutralization of the acidic catalyst after the reaction has taken place can be carried out with inorganic bases, for example NaOH, ROH, R2C03, Na2CO3, or organic bases, for example trimethyl-amine, triethylamine, dimethylcyclohexylamine or ~1 8060~

pyridine. In principle, a separate neutralization is not necessary, since, in the subsequent operation, the alkoxylation of the basic structure is carried out under base catalysis.
The course of the acetalization/transacetalization can be monitored and quantified from the amountsof water/-alcohol distillate obtained.
The products obtained may contain certain amounts of higher oligomers, i.e. oligoglycosides, as secondary constituents.
The compounds are subsequently alkoxylated. The reaction is carried out with ethylene oxide and/or propylene oxide (EO/PO) in a conventional manner using a catalyst. The products formed can be random mixtures of EO/PO or a group composed of up to three uniform blocks of these alkylene groups.
The degrees of alkoxylation are between > 0 and 30, preferably 5 and 20. The values of v + w and x + y are customarily averages.
The pH-sensitive surfactants of the formula (I) are generally useful as surface-active substances for industrial purposes and have a multiplicity of technical application possibilities. Of particular note is their use in cleaning baths of the metal industry for degreasing metal parts and also in the industrial cleaning of glass bottles, i.e. in particular in automatic cleaning processes.
These purposes require in particular surfactants which withstand the highly alkaline conditions of the cleaning 2180~0~

baths, which are low-foaming and which ensure good wetting of hard surfaces.
The concentration of the acid-cleavable surfactants is not critical and often is from 0.1 to 70% by weight, based on the preparation. Other customary constituents of the preparation are well known. A typical constituent is water.

- 7a -218060~
- 8 - O.Z. 4956 Setting the cleaning baths to an acid pH range of 0.5 - 6 will cleave the surfactants claimed herein and cause them to lose their surface-active character, as a result of which the soil emulsions break and form two phases.

S Preparation examples Example 1 490 g (2.5 mol) of methyl-~-D-glucopyranoside and 575 g (2.5 mol) of lauraldehyde dimethyl acetal were initially charged to a 2 l three-neck flask under a protective gas.
Following addition of 1.0 g of p-toluenesulphonic acid, the reaction batch was gradually heated to temperatures of 60 - 90C and the methanol formed was collected. To ensure a uniform production of methanol and thus a uniform reaction, a vacuum was applied and gradually reduced down to 20 mbar, according to the amount of distillate collected. After 3 - 6 hours the theoretical amount of methanol had been collected.

After transfer to an autoclave, the reaction product was admixed with 0.1 - 0.2% by weight of sodium hydroxide and carefully dewatered. This is followed by a reaction with ethylene oxide (about llO0 g = about lO mol of EO/mol of starting material) at temperatures of 90 - 140C. After the desired amount of ethylene oxide had been taken up, the reaction batch was allowed to cool down, neutralized with lactic acid and finally filtered hot.

Example 2 293 g (0.31 mol) of a butanolic butylglycoside solution (28% strength) and 57 g (0.31 mol) of lauraldehyde solution were initially charged to a 2 l three-neck flask under a protective gas. Following addition of 1.8 g of p-toluenesulphonic acid, the reaction batch was gradually heated to temperatures of 60 - 90C and the water of reaction formed was collected as an azeotrope with ~- _ g _ O.Z. 4956 butanol under a vacuum of 250 - 20 mbar. After the theoretical amount of water had been eliminated, the residual butanol was condensed and the reaction product was transferred to an autoclave. Following addition of 0.1 - 0.2~ by weight of sodium hydroxide, the batch was carefully dewatered. This was followed by reaction with ethylene oxide similarly to Example 1 using about 10 mol of EO/mol of starting material.

Application properties Foaming capacity and foam stability were determined in accordance with DIN 53902 in tap water (TW) at 20 - 60C
using aqueous mixtures having an active content of 0.1 g/l. The vessel (cylindrical shape, capacity 1000 ml) was in each case made up to a volume of 200 ml. The foam heights were read off after 60 beats and a subsequent standing time of 30 and 300 seconds.

The results (see table) reveal that, according to the foam test, the in-test compounds are all to be classed as very weak foamers.

~he wetting capacity was determined in line with DIN-ISO
8022. In each case concentrations of 1.0 g of active content/l of tap water were investigated at 20 and 60C, and the reported values are each averages of 10 measure-ments.

For the determination of the contact angle on PP see "Seifen-Ole-Fette-Wachse - Vol. 108 - No. 15/1982".

-- - 10 - O.Z. 4956 Table:

Com- Foam eest Wetting Contact angle pound Foam heights (in test decresse on PP in DM
ml) water (in 1) at 20C at 60C Sink time Conc. Conc. Conc.
(sec) in 0.1 1.0 10 TW g/l g/l g/l se sec sec sec C C
c E~. 1 60 50 20 10 >300 85 20 46 48 Ex. 2 50 40 10 0 59 49 21 3S 41

Claims (13)

1. An acid-cleavable alkylglycoside-based surfactant of the general formula:

(I) (wherein:
R1 represents an unbranched or branched alkyl or alkenyl group having 1 to 20 carbon atoms, R2 represents an alkyl group having 6 to 20 carbon atoms, G1 represents (EO)v(PO)wH, G2 represents (EO)x(PO)yH, where EO represents an ethyleneoxy group and PO represents a propyleneoxy group, and v, w, x and y are each such a number that the total of v and w is 0 to 30, the total of x and y is 0 to 30 and the total of v, w, x and y is at least 1).

2. The surfactant according to claim 1, wherein R1 denotes an alkyl group having 1 to 14 carbon atoms.

3. The surfactant according to claim 1 or 2, wherein G1 represents (EO)vH and G2 represents (EO)xH and v and x are each 0 to 30.

4. The surfactant according to any one of claims 1 through 3, wherein the total of v and x is 5 to 20 and w and y are each 0.

5. The surfactant according to claim 1, wherein:
R1 represents a C1-C4-alkyl group or an unbranched C8-C14-alkyl group, R2 is as defined in claim 1, G1 is (EO)vH, G2 is (EO)xH, and v and x are each a number of from 1 to 30.

6. The surfactant according to claim 5, wherein R1 represents a C1-C4-alkyl group.

7. A process for producing the surfactant as defined in any one of claims 1 to 6, which comprises:
reacting an alkylglycoside of the formula:

(III) (wherein R1 is as defined in any one of claims 1 to 6) with an aldehyde or diacetal of the formula:

R2?CHO or (wherein R2 is as defined in any one of claims 1 to 6, and R3 is a C1-C4-alkyl group) at a temperature of 50 to 200°C in a vacuum in the presence of a catalytic amount of an acid, to form a cyclic acetal of the formula:

(II) (wherein R1 and R2 have the meanings given above);
and alkoxylating the cyclic acetal of the formula (II) with ethylene oxide, propylene oxide or a random or block combination thereof in the presence of a catalyst.

8. A cleaning bath for degreasing metal parts, which contains the surfactant as defined in any one of claims 1 through 6.

9. A method which comprises cleaning glass bottles using the surfactant as defined in any one of claims 1 through 6.

10. The use of the acid-cleavable surfactant according to any one of claims 1 to 6 for an industrial purpose.

11. The use of the acid-cleavable surfactant according to any one of claims 1 to 6 in a washing and cleaning agent.

12. The use of the acid-cleavable surfactant according to any one of claims 1 to 6 in an automatic cleaning process.

13. The use of a preparation containing 0.1 to 70% by weight (based on the total amount of the preparation) of the acid-cleavable surfactant according to any one of claims 1 to 6 in a washing and cleaning agent.